There are already in existence various types of polytetrafluoroethylene seals and also various types of dual lip seals, some of which use polytetrafluoroethylene for at least one of the lips. However, most of these rely on clamping a polytetrafluoroethylene washer or wafer into a case, and those that do involve some bonding, usually bond only a single-lip seal. Clamping always involves the possibility of leakage and also involves a somewhat expensive assembly operation. That type of assembly operation can be eliminated when the entire seal is molded in a single operation. A molded seal can easily be assembled into a unitized seal or used without unitization, depending on which would be preferable for a particular use.
An important difficulty in the way of providing such a bonded dual-lip seal with polytetrafluoroethylene sealing edges, is that heretofore no economical process for achieving this molding has been provided. This is particularly true when the seal is to have one lip that is spring urged while the other lip is a wafer-type lip. The present invention makes this one-step molding possible.
Thus, it is an object of the present invention to provide a unitary molded dual-lip seal having polytetrafluoroethylene bonded to an elastomer and serving as the sealing surface for both lips.
Another object of the invention is to provide a practical method for making such a dual lip type of seal.